There's a line in one of the verses which I don't quite understand.

It's here:

'Twas England bade our wild geese go
That small nations might be free
Their lonely graves are by Suvla's waves
On the fringe of the grey North Sea'

How far does the fringe of the North Sea stretch to be anywhere close to Suvla Bay on the Aegean coast of the Gallipoli peninsula in European Turkey, south of the Gulf of Saros?